While titled "Talk to your Messenger Contacts on Skype" this blog post by Tony Bates (President, Skype division, Microsoft) is more than interoperability – Messenger is being retired in 1Q2013:
We’ve got good news to share! Skype and Messenger are coming together. Millions of Messenger users will be able to reach their Messenger friends on Skype. By updating to Skype, Messenger users can instant message and video call their Messenger friends.
This effort started with the release of Skype 6.0 for Mac and Windows a few weeks ago, which allows you to sign into Skype using a Microsoft account. Now Messenger users just need to update to the latest version of Skype, sign in using a Microsoft account, and their Messenger contacts will be there.
Our goal remains to deliver the best communications experience for everyone, everywhere. We want to focus our efforts on making things simpler for our users while continuously improving the overall experience. We will retire Messenger in all countries worldwide in the first quarter of 2013 (with the exception of mainland China where Messenger will continue to be available).
One of the perils of a large company is too many overlapping products so this seems like a wise move since Skype is bigger and has the momentum while Messenger is declining, but getting 100 million plus Messenger users to convert should be exciting.